The present invention relates to apparatus for testing for the occurrence of sheathing failures in fuel pins of a nuclear reactor cooled by liquid metal. Such apparatus is usually referred to as "Failed Fuel Detection Apparatus".
The general approach to this subject has been the use of coolant sampling pipes (one for each asembly of fuel) which are terminated at respective ports of a selection valve having a rotating selection arm with a rubbing seal which selects for measurement in sequence the coolant appearing at the ports in the valve. British patent specification No. 1,237,536 exemplifies this approach. A first pump is provided which draws coolant along the sampling pipes and a second pump is shown which draws coolant along the selection arm to delayed neutron counters.
However the rubbing seal is a point of weakness. Its failure could result in failure of the sampling system which would be difficult to replace.